Robust nonlinear control of atomic force microscope via immersion and invariance

This paper reports an immersion and invariance (I&I)–based robust nonlinear controller for atomic force microscope (AFM) applications. The AFM dynamics is prone to chaos, which, in practice, leads to performance degradation and inaccurate measurements. Therefore, we design a nonlinear tracking controller that stabilizes the AFM dynamics around a desired periodic orbit. To this end, in the tracking error state space, we define a target invariant manifold, on which the system dynamics fulfills the control objective. First, considering a nominal case with full state measurement and no modeling uncertainty, we design an I&I controller to render the target manifold exponentially attractive. Next, we consider an uncertain AFM dynamics, in which only the displacement of the probe cantilever is measured. In the framework of the I&I method, we recast the robust output feedback control problem as the immersion of the output feedback closed‐loop system into the nominal full state one. For this purpose, we define another target invariant manifold that recovers the performance of the nominal control system. Moreover, to handle large uncertainty/disturbances, we incorporate the method of active disturbance rejection into the I&I output feedback control. Through Lyapunov‐based analysis of the closed‐loop stability and robustness, we show the semiglobal practical stability and convergence of the tracking error dynamics. Finally, we present a set of detailed, comparative software simulations to assess the effectiveness of the control method.     

New multi‐standard dual‐wideband and quad‐wideband asymmetric step impedance resonator filters with wide stop band restriction

New multi‐standard wide band filters with compact sizes are designed for wireless communication devices. The proposed structures realize dual‐wideband and quad‐wideband characteristics by using a new skew‐symmetrical coupled pair of asymmetric stepped impedance resonators, combined with other structures. The first and second dual‐wideband filters realize fractional bandwidths (FBW) of 43.2%/31.9% at the central frequencies (CF) of 1.875/1.63 GHz, and second bandwidths of 580 MHz/1.75 GHz at CF of 5.52/4.46 GHz, respectively. The proposed quad‐band filter realizes its first/second/third/fourth pass bands at CF 2.13/5.25/7.685/9.31 GHz with FBW of 46.0%/11.4%/4.6% and 5.4%, respectively. The wide pass bands are attributed to the mutual coupling of the modified ASIR resonators and their bandwidths are controllable by tuning relative parameters while the wide stop band performance is optimized by the novel interdigital cross coupled line structure and parallel uncoupled microstrip line structure. Moreover, the quad band is generated by introducing the novel defected rectangle structure. These multi‐standard filters are simulated, fabricated and measured, and measured results agree well with both simulated results and theory predictions. The good in‐band and out‐of‐band performances, the miniaturized sizes and simple structures of the proposed filters make them very promising for applications in future multi‐standard wireless communication.     

Swelling and network parameters of high oil‐absorptive network based on 1‐octene and isodecyl acrylate copolymers

Crosslinked 1‐octene‐isodecyl acrylate copolymers were synthesized and evaluated for oil‐absorbency applications. The copolymer was crosslinked at different concentrations of ethylene glycol diacrylate (EGDA) and EG dimethacrylate (EGDMA) crosslinkers via catalytic initiation or by electron‐beam irradiation at a dose rate 80 kGy. The concentration of both crosslinkers was varied from 0.5 to 2%. The effects of the crosslinking conditions such as crosslinker concentration, method of polymerization and monomer concentrations on the conversion and gel fraction were examined through oil‐ absorption tests using petroleum crude oil. It was found that the oil absorbency was influenced mainly by the degree of crosslinking and the hydrophobicity of the copolymer units. The final equilibrium oil content, volume fraction of the polymer, and swelling capacity were determined at 298 K. The effective crosslinking density, average molecular weight between the crosslinks, and polymer–toluene interaction parameter were determined from stress–strain measurements. The crosslinking efficiencies of EGDA and EGDMA toward copolymers were determined. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 80–91, 2005     

Investigation of liquid maldistribution in trickle-bed reactors using porous media concept in CFD

A three-dimensional CFD model for simulating two-phase flow in trickle-bed reactors (TBRs) is presented. Based on porous media concept, a two-phase Eulerian model (rather than computationally demanding traditional three-phase Eulerian model) describing the flow domain as porous region is presented to understand and forecast the liquid maldistribution in TBRs under cold-flow conditions. The drag forces between phases have been accounted by employing the relative permeability concept [Sàez, A. E., Carbonell, R. G., 1985. Hydrodynamic parameters for gas-liquid cocurrent flow in packed beds. A.I.Ch.E. Journal 31, 52-62].The model predictions are validated against experimental data reported in literature, notably using the liquid distribution studies of Marcendelli [1999. Hydrodynamique, Transfert de Chaleur Particule-Fluide et Distribution des phases dans les Reacteurs a lit Fixe a Ecoulement a Co-courant Descendant de Gaz et de Liquide. Doctoral Thesis. INPL, Nancy, France]. Various distributor configurations reported therein have been recreated in the CFD model and sensitivity studies have been performed. Good agreement is obtained between the reported experimental results and this proposed first-principle based CFD model.Finally, the concept of distribution uniformity is discussed and applied to the CFD model predictions. The CFD model is subjected to a systematic sensitivity study in order to explore better liquid distribution alternatives.     

Letters of recommendation.

Discusses the goals and preparation of letters of recommendation and presents the results of a survey of 13 trainees who were to be the subject of recommendations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrospinning: An emerging technology to construct polymer-based nanofibrous scaffolds for diabetic wound healing

A chronic wound in diabetic patients is a major public health concern withsocioeconomic and clinical manifestations.The underlying medical condition of diabeticpatients deteriorates the wound through physiological,metabolic,molecular,and cellularpathologies.Consequently,a wound enters a vicious pathological inflammatory cycle.Many therapeutic approaches are in practice to manage diabetic wounds hence ensuringthe regeneration process.Polymer-based biomaterials have come up with hightherapeutic promises.Many efforts have been devoted,over the years,to build aneffective wound healing material using polymers.The electrospinning technique,although not new,has turned out to be one of the most effective strategies in buildingwound healing biomaterials due to the special structural advantages of electrospunnanofibers over the other formulations.In this review,careful integration of allelectrospinning approaches has been presented which will not only give an insight intothe current updates but also be helpful in the development of new therapeutic materialconsidering pathophysiological conditions of a diabetic wound.     

Greatly reduced leakage current and defect mechanism in atmosphere sintered BiFeO3–BaTiO3 high temperature piezoceramics

In current work, the effect of sintering atmospheres (N₂, air and O₂) on the structure, electrical properties, and defect mechanism of 0.8BiFeO₃–0.2BaTiO₃ lead-free piezoelectric ceramics has been investigated. X-ray diffractometer results indicated all the samples crystallized into the rhombohedrally distorted perovskite structure which was independent on the sintering atmospheres. Bi-containing impurity phases were observed in N₂ sintered samples while not appearing in other atmospheres. X-ray photoelectron spectrum analysis indicated more Fe²⁺ ions, which can result in high leakage current, were involved in N₂ sintered ceramics than that in O₂- and air sintered compositions. However, greatly reduced leakage currents were obtained in N₂ sintered ceramics which should be ascribed to the formation of secondary phases. The largest polarization and lowest leakage current were obtained in the sample sintered in N₂ (2 h), which owned the optimal ferroelectric, piezoelectric, and electromechanical properties with piezoelectric constant d ₃₃ = 98 pC/N, planar electromechanical coupling factors k _p = 26.1 %, remnant polarization P _r = 25.7 µC/cm², coercive field E _c = 74.6 kV/cm, and a high Curie temperature T _c = 632 °C, respectively.     

Effect of radiation and soaking on trypsin inhibitor and protein content of chickpea (Cicer arientinum L.)

Composition of Ascochyta-blight resistant chickpea for proximate components, vitamins, energy and trypsin inhibitor, was determined. The influence of irradiation and soaking at ambient temperatures (25–35°C) on trypsin inhibitor activity (TIA) and protein content of chickpea, was investigated. A significant linear relation (r = ?0.960 to ?0.987) was found between the loss of TIA and soaking time of irradiated and unirradiated seeds (p < 0.05) and the rate of loss increased with increasing radiation dose (0.25–1.00 kGy). However, effect of radiation alone was negligible. Maximum decrease (30.7%) in TIA (from 330.0 to 228.6 TIU/g) occurred during soaking for 12 h of 1.00 kGy sample. The protein contents increased from an initial value of 21.7% to 23.4% and 22.7% as a result of soaking for 12 h in tap and distilled waters respectively. Radiation treatment exhibited little or no effect.     

Protein isolates from Egyptian sweet potato leaves

The optimum conditions for protein extraction from sweet potato leaves were studied. The results obtained led to the following conclusions: pH 10 was found to be the best pH for maximum protein recovery after 4 h of extraction using distilled water in a ratio of 20:1 (v/w) solvent to sweet potato leaf powder; to increase the yield of the extractable protein (leaf protein concentrate, LPC) it was necessary to double the extraction steps. After extraction, the protein was precipitated according to its isoelectric point which was found at pH 4. The LPC yielded from sweet potato leaves had less value of antinutritional factors than found initially in the leaves. Also, the functional properties of the isolated LPC were studied: Oil holding capacity of LPC was higher than water holding capacity of the same protein, also it was higher than oil holding capacity of the albumin. The coagulated protein value of the LPC was much lower than that of albumin. The foaming capacity of LPC at pH 7 was higher than that found at pH 4 and both were much lower than those of albumin. On the other hand the foam of LPC was more stable at pH 7 than that found at pH 4.